Flexible circuit board interconnection and methods

ABSTRACT

Embodiments of the invention include flexible circuit board interconnections and methods regarding the same. In an embodiment, the invention includes a method of connecting a plurality of flexible circuit boards together comprising the steps applying a solder composition between an upper surface of a first flexible circuit board and a lower surface of a second flexible circuit board; holding the upper surface of the first flexible circuit board and the lower surface of the second flexible circuit board together; and reflowing the solder composition with a heat source to bond the first flexible circuit board and the second flexible circuit board together to form a flexible circuit board strip having a length longer than either of the first flexible circuit board or second flexible circuit board separately. In an embodiment the invention includes a circuit board clamp for holding flexible circuit boards together, the clamp including a u-shaped fastener; a spring tension arm connected to the u-shaped fastener; and an attachment mechanism connected to the spring tension arm. Other embodiments are also included herein.

This application is a continuation application of U.S. application Ser.No. 14/506,251, filed Oct. 3, 2014, which is a continuation applicationof U.S. application Ser. No. 13/158,149, filed Jun. 10, 2011, now U.S.Pat. No. 8,851,356, which is a continuation-in-part of U.S. applicationSer. No. 12/372,499, filed Feb. 17, 2009, now U.S. Pat. No. 7,980,863,which claims the benefit of U.S. Provisional Application No. 61/028,779,filed Feb. 14, 2008, and U.S. Provisional Application No. 61/037,595,filed on Mar. 18, 2008, the contents of all of which are hereinincorporated by reference. U.S. application Ser. No. 13/158,149, filedJun. 10, 2011 is also a continuation-in-part of U.S. application Ser.No. 12/406,761, filed Mar. 18, 2009, now U.S. Pat. No. 8,007,286, whichclaims the benefit of U.S. Provisional Application No. 61/037,595, filedon Mar. 18, 2008, and U.S. Provisional Application No. 61/043,006, filedApr. 7, 2008, the contents of all of which are herein incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to flexible circuit boards. Morespecifically, the present invention relates to flexible circuit boardinterconnections, methods regarding the same, and apparatus regardingthe same.

BACKGROUND OF THE INVENTION

In some applications using electronic circuit boards, it is useful tojoin circuit boards together for the purpose of continuing an electricalcircuit. By way of example, it can be useful to join circuit boardstogether in Solid State Lighting (SSL) or LED Lighting applications. SSLcircuits are an extremely important application as SSL is more efficientin converting electricity to light than incandescent, fluorescent, andcompact fluorescent systems.

Conventional reflow soldering or wave soldering techniques and equipmentprovide for the batch processing of individual or panelized circuitboards. Conventional processing methods with reflow or wave solderingequipment are based on the soldering of individual or panelized circuitboards. Individual or panelized circuit boards are prepared with solderpaste, populated with various electronic components and then processedthrough a reflow or wave solder oven. Soldering is achieved in theconventional way through the control of heating profiles and travelthrough the oven typically along a conveyor system.

SUMMARY OF THE INVENTION

Embodiments of the invention include flexible circuit boardinterconnections and methods regarding the same. In an embodiment, theinvention includes a method of connecting a plurality of flexiblecircuit boards together comprising the steps applying a soldercomposition between an upper surface of a first flexible circuit boardand a lower surface of a second flexible circuit board; holding theupper surface of the first flexible circuit board and the lower surfaceof the second flexible circuit board together; and reflowing the soldercomposition with a heat source to bond the first flexible circuit boardand the second flexible circuit board together to form a flexiblecircuit board strip having a length longer than either of the firstflexible circuit board or second flexible circuit board separately.

In an embodiment the invention includes a circuit board clamp forholding flexible circuit boards together, the clamp including a u-shapedfastener; a spring tension arm connected to the u-shaped fastener; andan attachment mechanism connected to the spring tension arm.

This summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE FIGURES

The invention may be more completely understood in connection with thefollowing drawings, in which:

FIG. 1 is a schematic top view of two circuit boards connected withconnector in accordance with various embodiments herein;

FIG. 2 is a schematic top view of a top profile view of a connectorboard in accordance with various embodiments herein;

FIG. 3 is a schematic top profile view of an outline of routed panelready for component assembly and cutting in accordance with variousembodiments herein;

FIG. 4 is a schematic top profile view of a panel outline with endssheared off to expose boards in accordance with various embodimentsherein;

FIG. 5 is a schematic top profile view of panels joined by connectors inaccordance with various embodiments herein;

FIG. 6 is a schematic top profile view of circuit strips afterseparation in accordance with various embodiments herein;

FIG. 7 is a schematic top profile view of soldering of connector jointin accordance with various embodiments herein;

FIG. 8 is a schematic side profile view of an overlapping joint betweenboards in accordance with an alternate embodiment herein;

FIG. 9 is a schematic top profile view of panels joined by overlappingjoints in accordance with various embodiments herein;

FIG. 10 is a schematic top profile view of potting material used tostrengthen and protect connection joints in accordance with variousembodiments herein;

FIG. 11A is a schematic top view of top board pads and holes inaccordance with various embodiments herein;

FIG. 11B is a schematic bottom view of top board pads and holes inaccordance with various embodiments herein;

FIG. 12 is a schematic top view of bottom board receiving pad geometryin accordance with various embodiments herein;

FIG. 13A is a schematic top view of an assembled board prior to joiningin accordance with various embodiments herein;

FIG. 13B is a schematic top view of joined boards in accordance withvarious embodiments herein;

FIG. 14 is a schematic side view of a joint assembly of a flexible stripwith curvature in accordance with various embodiments herein;

FIG. 15 is a process flow diagram for construction of multi-boardassemblies in strip or matrix form in accordance with variousembodiments herein.

FIG. 16 is a schematic top view of a plurality of circuit boards withholding apparatus in accordance with various embodiments herein.

FIG. 17 is a schematic view of two circuit boards with solder pad andplated hole features in the top circuit board and with mating solder padfeatures on the bottom circuit board in accordance with variousembodiments herein.

FIG. 18 is a schematic view of two circuit boards with prepared solderpads prior to attachment in accordance with various embodiments herein.

FIG. 19 is a schematic view of a successful solder joint resulting fromreflow soldering of a prepared lap joint held by an apparatus and reflowor wave soldered in accordance with various embodiments herein.

FIG. 20 is a schematic view of a circuit board clamp in accordance withvarious embodiments herein.

FIG. 21 is a schematic view of a circuit board clamp in accordance withvarious embodiments herein.

FIG. 22 is a schematic view of a plurality of top and bottom circuitboards each as part of an array of circuit boards arranged parallel toone another with electronic components prepared for soldering inaccordance with various embodiments herein.

FIG. 23 is a schematic illustration showing the solder connecting aplurality of long continuous circuit boards forming circuit board stripsin accordance with various embodiments herein.

FIG. 24 is a schematic top view of a plurality of circuit board clampsholding top and bottom circuit boards together in accordance withvarious embodiments herein.

FIG. 25 is a schematic bottom view of a plurality of circuit boardclamps holding top and bottom circuit boards together in accordance withvarious embodiments herein.

FIG. 26 is a schematic view of a circuit board with circuit board clampsallowing for a visual inspection step in accordance with variousembodiments herein.

FIG. 27 is a schematic view of a reflow solder oven with conveyor beltfeeds in and out of the machine in accordance with various embodimentsherein.

FIG. 28 is a schematic view of a wave solder machine with feeds in andout of tank in accordance with various embodiments herein.

FIG. 29 is a flow diagram of a method with unpopulated, pre-populated,and pre-populated/soldered plurality of circuit boards in accordancewith various embodiments herein.

FIG. 30 is a schematic top view of top circuit boards and bottom circuitboards ready for attachment that are pre-populated and pre-soldered withelectronic components.

FIG. 31 is a schematic top view of top circuit boards and bottom circuitboards ready for attachment with electrical component positions that areleft unpopulated.

FIG. 32 is a schematic view of a continuous plurality of solderedpanelized circuit boards in accordance with various embodiments herein.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawings, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to cover modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention described herein are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather, the embodimentsare chosen and described so that others skilled in the art canappreciate and understand the principles and practices of the presentinvention.

All publications and patents mentioned herein are hereby incorporated byreference. The publications and patents disclosed herein are providedsolely for their disclosure. Nothing herein is to be construed as anadmission that the inventors are not entitled to antedate anypublication and/or patent, including any publication and/or patent citedherein.

It can be advantageous to construct long continuous circuits for use inlinear lighting systems or other configurations constructed from linearstrip systems. While certain methods can provide for the creation oflong linear SSL circuits through manual soldering, these methods do notaddress how to build long continuous strips utilizing conventionaltechniques and equipment such as reflow soldering or wave solderingequipment.

While the soldering of individual electronic components onto circuitboards is readily accomplished with reflow or wave soldering equipment,the soldering together of individual or panelized circuit boards to eachother using this same equipment and standard techniques is not easilyaccomplished for a number of reasons.

First, the solder connection of individual or panelized circuit boardsto each other using conventional reflow or wave soldering equipment andtechniques requires that the boards be held in some fashion throughoutthe entire soldering processes. The method and apparatus for holdingneeds to provide for adequate contact between the boards to allow theheated solder to flow and wet between the boards and intended solder padareas.

The holding method and apparatus must also not interfere with theheating of the boards and solder paste material. Methods or apparatuslaid directly on top of board solder joints would tend to interfere withheat flow to the solder joints resulting in incomplete to weak solderjoints. Apparatus constructed from materials affected by the liquidsolder would tend to interfere with the solder joint or become trappedas part of the joint interfering with the quality of the joint.

The holding method and apparatus also needs to provide adequatealignment of the circuit boards in order to maintain the relativeposition of solder pads through the entire process. Wave solderingapproaches where waves of molten solder are passed over the boards isalso particularly challenging for maintaining alignment. Reflowsoldering techniques present challenges in alignment as the solderpasted circuit boards moving down a conveyor can be easily knocked outof position if simply laid onto of one another. Apparatus placeddirectly on top of boards would tend to interfere with heat flow andlimit visual inspection of solder joint quality. Heating profiles alongthe conveyor along with the flow of solder present further challenges asparts move and change shape due to thermal expansion and contractionduring heating and cooling through the reflow heating cycle along theconveyor. Parts would also need to be held from movement due to changesin surface tension as solder flux is heated and the liquid solder flowsout over the board and throughout the intended solder joint. Soldercooling from liquid to solid in the later stages of the reflow heatingcycle would further add force and movement to boards.

It would be further advantageous if the holding method and apparatus didnot interfere with visual inspection of solder joints whether manual orautomated. Large or opaque clamping apparatus would tend to prevent anyvisual inspection of the solder joint complicating inspection andquality control. Additionally, it would be advantageous that the holdingmethod be removable so as to not interfere with the end use of theresulting electronic circuit.

Embodiments herein include a method for creating long and longcontinuous circuit strips utilizing reflow or wave solder processingequipment and techniques. Further included are methods for holding aplurality of circuit boards and an apparatus for holding a plurality ofcircuit boards together during reflow or wave solder processing for thepurpose of constructing reliable and repeatable solder joints betweenthe circuit boards.

In some embodiments a method for creating long and long continuouscircuit strips by which a plurality of bottom circuit boards and aplurality of top circuit boards are prepared with solder paste, alignedfor connection and held in place with a holding apparatus and processedthrough reflow or wave soldering process. The method disclosed addressesthe connection of populated circuit boards with solder paste andelectronic components for soldering, the connection of unpopulatedplurality of circuit boards for later population with electroniccomponents through a secondary soldering process and the connection ofpre-populated and pre-soldered plurality of circuit boards for solderingof the board-to-board connection only.

In some embodiments a method is included for holding a plurality ofcircuit boards together that provides for alignment of mating solderlocations held in position throughout a reflow or wave solderingprocess. The embodiment includes a plurality of top circuit boards (a)and plurality of bottom circuit boards (b). Top circuit boards (a)including solder pad features with plated holes through the top board atpad locations allow solder and heat to flow down into the connectionboth to facilitate solder connection and to enable rapid connection.

The method of holding applies a downward force on top of a preparedjoint near the intended solder location point and an opposing downwardforce on the bottom of a prepared joint directly below the intendedsolder location. The forces are separated by a short distance and resultin a moment force at the prepared solder joint connection. The appliedforces and resulting moment force create sufficient friction forcebetween the top and bottom circuit boards to resist movement due tolateral or longitudinal forces typical in reflow or wave soldering andare therefore sufficient to maintain alignment of the top board andbottom board pad locations throughout the process.

Some embodiments herein are directed to an apparatus for holding aplurality of circuit boards together to provide for alignment of matingsolder locations held in position throughout a reflow or wave solderingprocess. The apparatus in some embodiments is in the form of a circuitboard clamp. The circuit board clamp can include a fastener, such as au-shaped fastener, to apply pressure to a plurality of top circuitboards and bottom circuit boards. The circuit board clamp can alsoinclude a spring tension arm connected to the u-shaped fastener. Inaddition, an attachment mechanism can be connected to the spring tensionarm on the opposite end from the fastener. The attachment mechanism canserve to provide attachment to the lower circuit boards. In someembodiments, the attachment mechanism is a hook. The spring tension armcan provide spring force between the fastener end and the attachmentmechanism.

In some embodiments, a method for creating long and long continuouscircuit strips utilizing reflow or wave solder processing equipment andtechniques is included. Further included are methods for holding aplurality of circuit boards and an apparatus for holding a plurality ofcircuit boards together during reflow or wave solder processing for thepurpose of constructing reliable and repeatable solder joints betweenthe circuit boards.

With reference to FIG. 1, a schematic top view of two circuit boardsconnected with a connector in an embodiment is shown. Circuit boards 5and 6 are shown joined with connector board 2 to create LED circuit 100.While the embodiment shown in FIG. 1 is directed towards flexiblelighting circuit boards and more directly towards flexible LED circuitboards, it will be appreciated that the scope of embodiments herein arenot limited to flexible lighting circuit boards and can include manydifferent types of circuit boards.

While connector board 2 is shown coupling the top surfaces of circuitboards 5 and 6 it is fully contemplated connector board 2 could becoupled between circuit boards 5 and 6 in most any fashion including onthe bottom surface of circuit boards 5 and 6 and overlapping between atop surface and a bottom surface. Circuit boards 5 and 6 are shown withcomponent pads 4 for receiving LEDs or other components. Connector board2 has plated through holes 1 disposed in conductive metal pads 27.Plated through holes 1 allow solder to flow through to connect circuitboards 5 and 6 as will be discussed in more detail below.

With reference to FIG. 2, a top profile view of a connector board in anembodiment is shown. Connector board 2 consists of a thin circuit board200 comprised of two electrically conductive layers 202 with a thinelectrical isolating material 204 sandwiched in between. In someembodiments, the conductive layers can be made of a conductive metal invarious thicknesses. By way of example, in some embodiments, theconductive layers can be made of copper. In a particular embodiment, theelectrically conductive layers are 2 oz. copper. It will be appreciatedthat many different materials can be used for the electrical isolatingmaterial. Such materials can have various thicknesses. In someembodiments, the electrical isolating material can be fiberglass. In aparticular embodiment the electrical isolating material is 0.012 inchthick fiberglass composite material.

Circuit paths 10 of various designs can be etched into the top and/orbottom conductive layers to produce the circuit conductive paths. Platedthrough holes 1 can be added at metal pads 27 and plated through withconductive metal to form a connection between top and bottom. Thinlayers of non-conductive solder repelling material 11 (solder masks) canbe added to the top and bottom of the board to restrict the movement ofsolder and protect the circuit paths from the pads.

With reference to FIG. 3, a top profile view of an outline of a routedpanel ready for component assembly and cutting in an embodiment isshown. Panels 102 of thin, flexible printed circuit boards can befabricated and routed so there is some amount of material 12 remainingto keep multiple parallel boards 13 in a parallel array. The material 12outside of the circuit board array further stiffens panel 102 and maycontain alignment marks or tooling holes for mechanical handling andalignment. Tabs 16 in a repeating pattern can be used to hold circuitboards 13 together. Routed slits 14 between tabs 16 can be used tomaintain mechanical alignment during assembly.

Panels 102 can be configured to allow them to be cut with a conventionalshear, scissors, or other cutting device at any of several locationsenabling later trimming to length or separation. It is fullycontemplated panels 102 could be laser cut as well to obtain circuitboards 5 and 6. Circuit boards 5 and 6 can be part of panels 102 asindicated by circuit board location 13. Electrical components, includingLED emitters and optionally thin board connectors can be assembled ontopanels 102 by conventional methods of electronic solder assembly. Insome embodiments, the connector pad geometry can be incorporated intothe board design so an additional connector board is not required,rather circuit boards 5 and 6 can be directly fastened together.

With reference to FIG. 4, a top profile view of a panel outline withends sheared off to expose boards is shown in accordance with anembodiment. As shown, sheared panel 103 frees up one or both ends 106and 104 of each printed circuit board 13. In some embodiments, this canbe done during the original panel fabrication. In some embodiments, aportion of the frame 19 may be retained to add stiffness to the assemblyand may contain alignment marks and tooling holes used to maintainmechanical alignment during assembly.

With reference to FIG. 5, a top profile view of panels joined byconnectors in an embodiment is shown. A free end 104 of one panel can bebutted against a free end 106 of the other so several circuit boards canbe joined by soldering or welding, thus forming a longer assembly withthe same characteristic of parallel strips. Depending on desired length,the process can be repeated by adding additional panels 103 to anelongated panel made up of multiple panels 103. After the desired lengthis attained, the strips can be separated by shearing any remainingconnecting material. As the long strips are joined, lined thermaladhesive tape 28 (FIG. 8) can be affixed to the bottom of the strips ina continuous action. The exposed liner (not shown) can be later removedduring application of the joined strips to a fixture or permanent mount.The addition of thermal adhesive tape 28 can occur just before or afterpanels 103 are joined together. The resulting elongated strips can thenbe wound onto large diameter reels so they can be easily protected,transported, and stored; ready for final assembly onto heat sinks orlight fixtures. As an alternative, the strips can be short enough to bepackaged and shipped in flat form.

With reference to FIG. 6, a top profile view of circuit strips afterseparation in an embodiment is shown. As shown, circuit strips 20 can beseparated from panels 103. Connection point 21 connecting two or morecircuit strips can be a connector 2 as discussed above or an overlapjoint discussed in more detail below. LEDs 22 or other components can beadhered or placed on circuit strips 20 and circuit strips 20 canterminate at ends 23.

With reference to FIG. 7, a top profile view of soldering of a connectorjoint in an embodiment is shown. Connector board 2 can be flexibleenough to conform to normal variations of board thickness, solder heightand mechanical mounting height differences. In an embodiment, connectorboard 2 is shown to bend with a radius 42 of down to 1 inch (see FIG.14). The connector board 2 can allow heat and solder to easily flowthrough connector board 2 from top to bottom as heat is applied. Soldermay be introduced into through hole 1 at the top of connector board 2.Alternatively solder may be in paste or hard form deposited on receivingprinted circuit board 5 or 6, in which case solder will flow from bottomto top.

Electrically insulating layer 204 within the thin board is thin enoughto both enable a high degree of thermal conductivity and is able tomaintain high levels of electrical breakdown isolation. Electricalisolation between circuits is helpful to the general function of theconnector; however, the amount of isolation may be changed to conform tothe application requirements.

The material chosen for the electrical insulating layer can enhancethermal conductivity. In one embodiment the electrically insulatinglayer was chosen as a high temperature variant of FR4 fiberglass with aglass transition temperature of 170° C., although this is just oneexample and many other materials can be used. A higher than normaltemperature rating of the material can be used to gain more thermalmargin allowing for the very rapid heating (and probable overheatingduring manual assembly) of the thin boards due to their low thermalmass. Even higher temperature materials can be used in the case highermelting temperature solders are to be used. In some embodiments, theinsulating layer is both durable at high temperatures and as highlythermally conductive as possible for this construction. Thermalconductivity can be helpful for the cases of solder iron or point heatsource assembly because it aides in rapid transfer of heat from the topside of the connector to the joints below.

Thin connector 2 board can add flexibility to connection 21, reducingstress at the solder joint associated with the use of rigid pins andother types of connectors. This is helpful to prevent tearing of theprinted circuit board pads on the board when bending stresses areintroduced. In one implementation, connector boards 2 can be used toform a continuous strip of boards which is then rolled into reel form.The bend radius 42 of this implementation can be 6 inches or greater.

Thin board substrate materials and thicknesses can be selected to handlesolder melt temperatures without delamination or damage. Alternatechoices for board insulating material can include materials such asTHERMAGON™ thermally conductive materials in cases where highertemperature resilience and higher thermal conductivity are needed. Anembodiment was developed for use with lower temperature solders(leaded). Copper pads can be on the bottom side of the connector orupper board 31 and can be designed to match the pads of the receivingboard 33—in spacing, in area, in thermal characteristics.

With reference to FIG. 8, a side profile view of an overlapping jointbetween boards in an alternate embodiment is shown. In the embodiment ofFIG. 8 no connector board 2 is used to connect circuit boards 5 and 6.The bottom side of an end of circuit board 6 is directly connected tothe top side of an end of circuit board 5. Conductive metal pads 27 canbe on the top side to receive heat (such as from a soldering iron 24,shown in FIG. 7) and provide a path for conduction through theelectrically insulating substrate and/or a plated through hole 1 toconductive metal pads 33 (shown for example in FIG. 12) on the bottom.The size of pads 30, 31 and 33 (FIGS. 11A, 11B and 12) factor into boththe quality of the connection and the mechanical stress the connectioncan sustain. In some embodiments, by embedding or closely connectingthrough holes 1 to pads 31, 38, the mechanical performance can beimproved. The metal plating and solder fill through hole 1 links topside pads 27 to bottom side pads 33 making the bottom side verydifficult to pull off (delaminate) from the insulating layer. Throughholes can be of various sizes. In some embodiments, the through holescan be about 0.036 inches in diameter to promote heat transfer, conductsolder and add enough structure to strengthen the joint. Lapped jointsadd strength by adding additional contact area, by reducing leverage,and by changing certain forces from shearing and tensile to compressive.

The interconnect aspect of FIG. 8 allows for the coupling of circuitboards without a connector board or any other device between them. Thuscircuit boards 5 and 6 can be created with ends 104 and 106 which havepads 30, 31 and 33 with though holes 1 to allow coupling of the circuitboards.

Copper conductors can be used for connecting pads 27 to be mated tocircuit path 10. Circuit path 10 can be printed in almost any pattern,such as those commonly used in circuit boards and can be patterned toreceive electronic components 4 such as LEDs 22, integrated circuits 36,or other electronic components. In some embodiments, the copperconductors can be very thick and wide to accommodate high currents. In aparticular embodiment 2 oz. copper was used with a conductor width of0.040 inch to enable a low voltage drop across the connector whencarrying up to 5 amps of current.

Copper foils are designed to maintain gap distances between connectionsfor electrical isolation. In an embodiment, voltage isolations of up to500 V were maintained by maintaining a distance of 0.025 inches betweencopper foils. By increasing the spacing, substantially higher isolationscan be achieved. Copper conductors can be run on top of or under theconnector insulating substrate, depending on requirements for isolation,current carrying capacity and protection. Connections and conductors areprotected from damage or shorting by being covered by the connector bodyor overlapping joint 26.

Connections and conductors can be further protected from moisture by thesimple addition of an under fill layer of potting material or anencapsulent or an overcoat of potting material 29 or encapsulent.Potting compounds or conformal coatings are commonly used in theindustry to provide this type of protection. This type of connector isparticularly suitable for these coatings because it is essentially flatwith no recesses or areas which must be protected from contact with thecoatings.

Plated through holes 1 located at pad positions 27, 30 and 31 throughconnector board 2 allow solder and heat to flow down into the connectionboth to facilitate solder connection and to enable rapid connection. Therate of heat transfer being increased by this structure has theadditional benefit of speeding up solder melting and cooling both duringmanual soldering and reflow processing. This can save time and result inbetter, more repeatable and stronger joints.

A number of experiments were conducted to determine solder wetting andflow paths for various pad geometries using the thin connectors insurface mount applications. After it is melted, solder tends to wet tothe metal pads 30 and exposed conductors of printed circuit boards 5 and6. It moves by capillary action to actively fill small gaps and spacesbetween pads 31 and 33, particularly pads in flat surface-to-surfacecontact. The high degree of adhesion and capillary action exhibited bysolder, combined with the mechanical weight of the thin board connectorcaused pads of connector board 2 and circuit boards 5 and 6 to pulltogether pushing remaining solder outward between pads 31 and 33. Ifsolder was applied in exactly the correct amount, the solder wouldsimply fill the joints. But even in small excess, the solder would pressoutside of the pad areas promoting shorts and lower electricalisolation. Holes, recesses or pockets between the pads were tried anddid take up the excess solder. However, the approach was to design inplated holes 1 within the area of the pads taking up the solder throughcapillary action, effectively pulling excesses into rather than out ofthe joint. In a particular embodiment, the holes were approximately 50%of the diameter of the pad, giving ample room for significant variancesin solder application. Though it will be appreciated that other holesize to pad diameter ratios can be used.

In some embodiments, plated holes 1 can be used as receptacles forsolder paste so connectors 2 could be ready for joining by heat alone.Once aligned to printed circuit boards 5 and 6, connector 2 (orselectively its pads) can be heated to cause the solder to begin meltingfor example using a soldering iron 24. By capillary action and wetting,the solder quickly flows down into the space between connector 2 andboard pads completing the joint. Flux and activating resins, which arecommonly incorporated into solder paste, are needed for high qualitysolder joints. In one embodiment, the same plated through holes 1 usedto store solder prior to thermal joining absorb excess solder. Further,the holes can be filled with either solder paste or separated layers ofhard solder and flux resin. In one embodiment, solder wire with a coreof flux resin can be press fit in holes 1 and sheared to match theconnector bottom surface 26. It was experimentally determined that thiswas another effective way of putting solder and flux into plated holes1. Sealing of solder paste in holes 1 at pad positions 27 and 26 can behelpful so paste remains fresh for later use. Sealing can include a thinsolder layer, a thin flux layer or a thin plastic or metallic peel offmaterial.

As part of the printed circuit board fabrication process, mask coatingscan be placed over top 11 and the bottom of the connector board (open atthe pads), reducing the opportunity for solder shorts and improving theappearance of the connector or overlapping joint. In some embodiments,the mask coating can be chosen to match the color and characteristics ofthe boards being jointed so to minimize the visibility of connectorboard 2. Connector board 2 can be implemented without mask coatings onthe top surface as this is less critical to the solder flow protectionfunction.

Connector boards 2 can be easily mechanically formed for vertical stepoffsets 41. In experiments run on these connectors 2, bends up to aright angle could be performed with the conductors (or any foilscrossing the bend) on the inside radius of the bend.

Connector boards 2 can incorporate other circuits, including pads andgeometries for wire or other conventional types of connectors, as wellas being able to incorporate terminations and active circuitry.Connector board 2 is particularly well suited because of its highlythermally conductive structure for power and heat creating circuits. Inone implementation, the circuitry included a high current driver (OneSemiconductor #NUD4001 operating at 24 VDC) along with an LED stringadded to the top side of the board. Both the top (FIG. 11a ) and bottomside (FIG. 11b ) of the board were designed with large metal (such ascopper) pads 30 and 31 that could translate heat through the thininsulating material by effectively creating a large area for heattransfer from the top copper layer through the less thermally conductiveinsulating layer and to the bottom copper layer. Further, a thermallyconductive adhesive tape 28 (e.g., 3M product #8810) can be applied tothe back side. The assembly can then be adhered to a heat sink 25. Theresulting structure was found to maintain excellent heat transfer to theheat sink, which is particularly important in high brightness LEDapplications.

Because this connector can be easily fabricated in many shapes, it canbe used for connection between boards directly abutted (FIG. 5) or somedistance apart. Also, since the conductors can be on either top orbottom, or embedded in a center layer, electrical isolation fromneighboring structures can be high and possible shorting points can bereadily avoided. Connector boards 2 are stackable and can be solderedone to another.

In cases where additional mechanical support is needed, the connectorcan extend well beyond the pad providing maximum overlap. It may benecessary to shape the connector or have it fabricated with clearanceholes if components on the underlying board may interfere. Connectorboard 2 can be fabricated with additional pads and holes (not connectedto the circuits) to give additional strain relief. Pad geometries maymatch existing pinned connectors to allow the option to alternate use ofa pinned connector or thin board connector. Thin connector boards may beused to join circuit boards into strips 20 or matrixes with multipleconnectors or connections 21 in each assembled length (See FIG. 6).

Thin connector boards can be overlapped for interconnection (See FIG.8). This is very useful if the connector board contains active circuitryand it is beneficial to connect multiple boards, such as in thefabrication of a continuous strip of boards (See, e.g., FIG. 6). Thethin connector boards can be highly advantageous to the assembly ofstrips consisting of multiple circuit boards (See FIG. 9). In apractical application, they can be used to make long circuit boardstrips of solid state lighting circuits (e.g., high power LED emittersused as the individual light sources), amongst other applications.

Thin circuit board 13 can include a thin, low thermal mass substratebase material comprised of two electrically conductive layers with athin, electrically isolating material sandwiched in between. In someembodiments, the conductive layers can be made of a conductive metal invarious thicknesses. By way of example, in some embodiments, theconductive layers can be made of copper. In a particular embodiment, theelectrically conductive layers are 2 oz. copper. It will be appreciatedthat many different materials can be used for the electrical isolatingmaterial. Such materials can have various thicknesses. In someembodiments, the electrical isolating material can be fiberglass. In aparticular embodiment the electrical isolating material is 0.012 inchthick fiberglass composite material. Circuit patterns of various designscan be etched into the top and bottom conductive layers to produce thecircuit conductive paths. Holes can be added at the pad locations andplated through with conductive metal to form a connection between topand bottom. Additional thin layers of non-conductive, solder repellingmaterial (solder masks) can be added to the top and bottom of the boardto restrict the movement of solder and protect the circuit paths awayfrom the pads.

Angled or other geometric patterns in the pad and copper conductors canbe included and can support connections for offset or angled printedcircuit boards. Multiple pad sets and associated conductor connectionscan be included and can allow for splitting of conduction paths.

The thin circuit board as described can be flexible enough to conform tonormal variations of board thickness, solder height, and mechanicalmounting height differences (See FIG. 14). Goals for high reliabilityconnections include robustness, both in mechanical strength and inintegrity of the electrical connection. By increasing the number of pads30, 31 and 33 used in the connector, mechanical strength was increased.Simple multiplication of the number of contacts added to the strength byspreading stress across the added contacts. Redundant parallel contactsreduce electrical resistance and add to the general integrity ofelectrical connection.

Intimate contact between metal pads with minimal fill layer of solderincreases joint 26 strength. A thick layer of solder decreases strengthbut adds some flexibility to the joint. Solder generally has a muchlower tensile and shear strength than the conductors it joins. Further,it tends to have a course crystalline structure and is susceptible tofracturing. However, a thin layer of solder between copper pads (usedthe pad material) is much less susceptible to fracturing both because ofsmaller (or incomplete) crystal formation, and because stresses aretransferred locally to the stronger copper, instead of into the solderitself.

Increasing the size of the pads 31 and 33 increases the strength bothbecause of the larger solder contact area, but also because of thelarger areas of contact and adhesion between pad and insulatingsubstrate. In multiple trials, larger pads consistently increased thestrength as measured in pull tests and in bending tests. Larger areas ofconductor surrounding exposed, soldered pad apertures increase thestrength both by offering more area for adhesion between the conductorand the insulating substrate, but also because they add to the conductorstructure.

Increasing the distance across a set of pads 37 or span increases thejoint strength against shear and rotational forces and torques. Shearand rotational forces (torques) are common highest during handling ofthe joined boards. Of particular use, the assembly of multiple boardsinto long strips presents the opportunity to put very high torques onthe joint connection because of the length and spring tension armadvantage. Preventing damage due to rotational forces is helpful tohaving reliable joints when the strips are packaged and used in theirmultiple forms including strips and continuous reeled lengths.

By increasing the distance of the pads from the overlapping edges of theboard, the inventors have found a decreased leverage on the individualconnections by converting stresses into surface pressures away from thejoint. By increasing the number of through holes 1 leading from topsurface to the pads below, an increase in the strength is discovered byadding more copper cylindrical connections and rivet like columns ofsolder fill linking top to bottom. Increased number of holes alsoincreases the probability of having a better percentage of solder fillbetween the boards. The choice of solder type and composition has adirect impact on joint strength. Lead baring solders have lower tensilestrength then their lead free counterparts. Higher tensile strengthincreases the fracture strength of the connection.

The application of tape or adhesive 28, across the bottom side of joint26, can further increase joint strength for handling. Viscous tapes actas a spring and dampener to certain stresses, moving forces away fromthe joint. The application of potting material 29 or other adhesives orcoatings of structure adds additional strength to joint 26 as well asprotection from mechanical damage and/or moisture (See FIG. 10).

In the areas of board overlap, excluding the conductive pad locations,adhesive applied between top and bottom board can be added to increasejoint strength. Thin board connectors 2 or thin circuit boards 13 and 39with overlapping joints 26 can be used to construct elongated strips ofmultiple circuit boards 20. Mass parallel construction of long circuitboard strips carrying high intensity LEDs for SSL applications has beendemonstrated using these connection types.

With reference to FIG. 15, a process flow diagram for construction ofmulti-board assemblies in strip or matrix form in an embodiment isshown. Process 300 starts at state 302 where circuit panels 102 arefabricated as discussed in detail above. At state 304 components, suchas LEDs are coupled to circuit boards 5 and 6, which are developed frompanel 102. If necessary, circuit joints 18 are exposed for assembly atstate 306. At state 308 board panels or arrays are joined by solder orwelding. At state 310 strip assemblies within the board panels or arraysare separated from each other. At state 312 individual strips can bejoined into longer strips or matrix (including, for example, some boardsarranged perpendicularly to one another) forms.

In some embodiments a method is included for creating long continuouscircuit strips in which a plurality of bottom circuit boards and aplurality of top circuit boards are mechanically and electricallyconnected together by way of a soldered lap joint connection. Thesoldered lap joint connection results from the processing of the bottomand top plurality of circuit boards through conventional reflowsoldering or wave soldering processes.

In reference to FIG. 16, the plurality of bottom circuit boards 1101 anda plurality of top circuit boards 1102 are aligned for connection with aprepared lap joint 1117 and held in place with a circuit board clamp1116 and processed through either conventional reflow or wave solderingprocesses. The method disclosed addresses the connection of populatedcircuit boards with solder paste and electronic components forsoldering, the connection of unpopulated plurality of circuit boards forlater population with electronic components through a secondarysoldering process and the connection of pre-populated and pre-solderedplurality of circuit boards for soldering of the board-to-boardconnection only.

In some embodiments a method is included for holding a plurality ofcircuit boards together that provides for alignment of mating solderpads held in position throughout a reflow or wave soldering process. Inreference to FIG. 16, a plurality of bottom circuit boards 1101 can beplaced onto a conveyor belt or table for advancing the boards into thereflow solder oven. A second plurality of top circuit boards 1102 can isplaced on top of the first plurality of circuit boards 1101 with somearea of overlap. The placement of the circuit boards is done with careto align the plurality of solder pad features of the top circuit boards1102 with the bottom circuit boards 1101 to create a prepared joint1117.

Referring now to FIG. 17, the alignment of the top and bottom pluralityof circuit boards is such that the solder pads 1010 on the top pluralityof circuit boards 1102 are aligned with the receiving solder pad 1011 onthe bottom plurality of circuit boards 1101. Top circuit boards 1102including solder pad features previously disclosed with plated holes1025 through the top board at the pad locations. Plated holes 1025 inthe top circuit board 1102 allow solder and heat to flow down into theconnection both to facilitate solder connection and to enable rapidconnection.

Referring now to FIG. 18, the top and bottom plurality of circuit boardsmay be prepared in advance with solder paste 1012 onto the solder padsof only the plurality of top circuit boards 1102, or with solder paste1012 onto the solder pads 1010 of the plurality of top circuit boards1102 and solder pads 1011 of the plurality of bottom circuit boards1101, or with solder paste 1012 onto the solder pads 1011 of only thebottom plurality of circuit boards 1101. In some embodiments, the amountof solder paste used is controlled with precision.

Referring now to FIG. 19, the resulting soldered lap joint connection1124 provides for a reliable mechanical and electrical board-to-boardconnection for the plurality of top circuit boards 1101 and bottomcircuit boards 1102 creating a long circuit board assembly 1301 (or longcircuit board strip). The process can be repeated by adding additionaltop circuit boards 1101 to the newly created long circuit board assembly1301 to create a long continuous circuit board assembly 1302 (in FIG.23) (or long continuous circuit board strip).

In some embodiments, an apparatus is included for holding a plurality ofcircuit boards together to provide for alignment of mating solderlocations and held in position throughout a reflow or wave solderingprocess. In some embodiments, this apparatus can be a circuit boardclamp. Referring to FIG. 20, the apparatus in some embodiments is in theform of a circuit board clamp 1116 with a fastener 1118, an attachmentmechanism 1119 and a spring tension arm 1120. The fastener 1118 appliespressure to a plurality of top circuit boards 1102 and bottom circuitboards 1101. The attachment mechanism 1119 attaches to the bottom of thetop circuit boards 1101 and a spring tension arm 1120 provides springforce between the fastener end 1118 and attachment mechanism end 1119.In some embodiments, the fastener 1118 is in the form of a u-shapedfastener. The fastener 1118 can include a top bar portion 2001, a bottombar portion 2003, and a interconnection member 2005 disposed between thetwo. In some embodiments, the top bar portion 2001 and the bottom barportion 2003 are substantially parallel to one another. In someembodiments, the spring tension arm 1120 has a major axis orientedsubstantially perpendicularly to the top bar portion 2003.

It will be appreciated that the circuit board clamp 1116 may take manyshapes in order to accommodate differing boards and connectorgeometries. The embodiment of FIG. 20 illustrates the form of thecircuit board clamp 1116 as constructed from small gauge wire. Theselection of a small gauge allows for the fastener end 1118 to easilyfit through a narrow routed slot 1121 in the bottom plurality of circuitboards 1102 and be rotated approximately 90 degrees at the intendedholding points on the top circuit board at point 1201 and on the bottomcircuit board at point 1202 on the overlapping boards (see FIG. 10). Thesmall gauge wire allows for the attachment mechanism end 1119 to passthrough the narrow routed slot 1121 in the top plurality of boards 1101.The resulting circuit board clamp 1116 provides the necessary forces asdescribed above to hold the top and bottom plurality of circuit boardsin alignment for processing through a reflow or wave solderingoperation.

A number of experiments were conducted on the circuit board clamp 1116embodiment. It was found that a reverse bend 1122 in the bottom barportion 2003 of the fastener 1118 improved the ability to hold the topcircuit board 1101 and bottom circuit board 1102 parallel to each other.The reverse bend 1122 is “reverse” in that it results in the distal endof the bottom bar portion 2003 being pointed away from the top barportion 2001 as shown in FIG. 21.

Parallel surfaces in the prepared solder joint 1117 were found toimprove solder wetting throughout the joint. Further experiments wereconducted on the attachment mechanism end 1119 of the circuit boardclamp 1116. It was found that a hook attached to the top circuit board1101 through the narrow routed slot 1121 away from the routed tabbetween boards 1123 eliminated the need for the circuit board clamp 1116to be sized specific to each board routing pattern 1121, 1123. In someembodiments, the attachment mechanism 1119 can comprise an attachmenthook 2007.

FIG. 24 is a schematic top perspective view of a plurality of circuitboard clamps 1116 holding top 1102 and bottom 1101 circuit boardstogether in accordance with various embodiments herein. In reference toFIG. 24, the method of holding involves the application of a downwardforce 1201 with circuit board clamp 1116 on the top of a prepared lapjoint 1117 of the top circuit board 1102 near the intended solder point1019, an opposing upward force 1202 on the bottom of a prepared lapjoint 1117 of the bottom circuit 1101 directly below the intended solderlocation 1020. The forces are separated by some lateral distanceresulting in a force moment at the prepared lap joint 1117 for solderconnection. The applied forces and resulting force moment createfriction force within the prepared joint. The resulting friction forceis sufficient to resist movement due to forces typical in reflow or wavesoldering processes and is therefore sufficient to maintain alignment ofthe top plurality of circuit boards 1101 and bottom plurality of circuitboards 1102 within the prepared lap joint 1117. FIG. 25 is a schematicbottom perspective view of a plurality of circuit board clamps 1116holding top 1102 and bottom 1101 circuit boards together in accordancewith various embodiments herein.

FIG. 26 is a schematic view of top 1102 and bottom 1101 circuit boardswith circuit board clamps 1116 illustrating how the circuit board clamps1116 allow for a visual inspection step of the through holes 1025 andsolder therein in accordance with various embodiments herein.

In reference to FIG. 27, a reflow soldering process is shown where aplurality of top circuit boards 1102 and a plurality of bottom circuitboards 1101 are held together in a prepared lap joint 1117 and placedonto a conveyor belt 1401 for feeding into reflow solder oven 1400. Theresulting reflow soldered long circuit boards 1301 and continuoussoldered circuit boards 1302 with soldered lap joints 1015 exit reflowsolder oven at conveyor belt 1402.

In reference to FIG. 28, a wave soldering process is shown where aplurality of top circuit boards 1102 and a plurality of bottom circuitboards 1101 are held together in a prepared lap joint 1117 and placedonto a wave solder machine 1410 feeder table 1411. The resulting wavesoldered long circuit boards 1301 and continuous soldered circuit boards1302 with soldered lap joints 1124 exit reflow solder oven at exit table1412.

Pre-Populated Circuit Boards

It will be appreciated that methods in accordance with embodimentsherein can be performed with unpopulated circuit boards, pre-populatedcircuit boards, and pre-populated and pre-soldered circuit boards. Byway of example, FIG. 22 shows an embodiment in which the top circuitboards 1102 and bottom circuit boards 1101 may be pre-populated withsolder paste 1012 b and electronic components 1013 as in conventionalpreparation of circuit boards for reflow or wave soldering on to thecircuit boards. The plurality of populated top circuit boards can thenbe prepared with solder paste 1012 at the solder pads 1010. Solder paste1012 may also be applied to the plurality of pre-populated bottomcircuit boards 1101 at pads 1011 although tests conducted indicated theaddition of solder paste on the bottom circuit board 1101 solder pads1011 was not necessary to achieve reliable solder joints 1124.

The plurality of pre-populated top circuit boards 1102 can then bealigned over the top of the plurality of pre-populated bottom circuitboard 1101 solder pads 1011 and held in place with an apparatus 1116creating a prepared lap joint 1117 (see e.g., FIG. 16) ready for reflowor wave solder processing. The resulting reliable soldered lap joint1015 (see, e.g., FIG. 23) can result in a long circuit board assembly1301 (FIG. 19). The process can be repeated by adding additional topcircuit boards 1101 to the newly created long circuit board assembly1301 to create a long continuous circuit board assembly 1302 (see, e.g.,FIG. 23). An example of one method for preparation, alignment,connection, soldering and removal for pre-populated circuit boards isdescribed in FIG. 29 (identified as “Process B—Pre-populated”). It willbe appreciated that soldering can include the steps of a heating cycle,solder flow, and a cooling cycle.

The alignment of the top and bottom plurality of circuit boards is aidedthrough initial visual alignment of the solder pad 1010 to solder pad1011 and board end 1016 and board alignment marks 1014. The top andbottom circuit board alignment for solder processing is then determinedby long board edge 1018 and circuit board clamp 1116. The resultingprepared joint 1117 is aligned and held in place with circuit boardclamp 1116 for reflow or wave soldering.

Pre-Populated and Pre-Soldered Circuit Boards

FIG. 30 shows a further embodiment in which the top circuit boards 1112and bottom circuit boards 1111 both may be pre-populated andpre-soldered with electronic components 1013 soldered onto the pluralityof circuit boards. In this embodiment the pre-populated and pre-solderedtop circuit boards 1112 can then prepared with solder paste 1012 at thesolder pads 1010. Solder paste 1012 can also be added to the pluralityof bottom circuit boards 1111, but was found to not be necessary toachieve reliable solder joints 1124. The plurality of pre-populated andpre-soldered top circuit boards 1112 are then aligned over the top ofthe plurality of pre-populated and pre-soldered bottom circuit boards1111 for soldering of the prepared lap joint 1117 (FIG. 16) ready forreflow or wave solder processing. The resulting reliable soldered lapjoint 1015 (FIG. 23) resulting in a long circuit board assembly 1301(FIG. 19). The process can be repeated by adding additional top circuitboards 1111 to the newly created long circuit board assembly 1311 tocreate a long-continuous circuit board assembly 1302 (FIG. 23). Anexample of one method for preparation, alignment, connection, solderingand removal of pre-populated and pre-soldered circuit boards isdescribed in FIG. 29 (identified as “Process C—Pre-Soldered”).

Unpopulated Circuit Boards

FIG. 31 shows a further embodiment included herein where the top circuitboards 1102 and bottom circuit boards 1101 can be left unpopulated andspecifically where electrical component positions 1017 can be leftunpopulated. The plurality of top circuit boards 1102 can be preparedwith solder paste 1012 at the solder pads 1010 for creation of preparedlap joint 1117. Solder paste 1012 can also be added to the plurality ofbottom circuit boards 1101, but was found to not be necessary to achievereliable solder joints 1124. The plurality of pre-populated andpre-soldered top circuit boards 1102 are then aligned over the top ofthe plurality of pre-populated and pre-soldered bottom circuit boards1101 for soldering of the prepared lap joint 1117 ready for reflow orwave solder processing. Referring to FIG. 32, the resulting reliablesoldered lap joint 1015 resulting in a long circuit board assembly 1311.The process can be repeated by adding additional plurality of topcircuit boards 1101 to the newly created long circuit board assembly1311 to create a long-continuous circuit board assembly 1312. An exampleof one method for the preparation, alignment, connection, soldering andremoval of unpopulated circuit boards is described in FIG. 29(identified as “Process A—Unpopulated”).

Experiments conducted during reflow soldering demonstrated a pluralityof circuit boards held by an apparatus 1116 in the form of a preparedjoint 1117 (FIG. 16) could be successfully soldered together into areliable solder joint 1124 (FIG. 19) providing mechanical and electricalconnection between the top circuit board 1102 and bottom circuit board1101.

A number of experiments were previously conducted to determine solderwetting and flow paths for various pad geometries using overlappedboards in surface mount applications. After melting, solder wets to themetal pads and exposed conductors of printed circuit boards. The soldermoves through capillary action to actively fill small gaps and spacesbetween upper and lower board pads, particularly pads in flatsurface-to-surface contact as previously disclosed. The high degree ofadhesion and capillary action exhibited by liquid solder, combined withthe mechanical force moment on the prepared joint 1117 (FIG. 24)provides for reliable soldering of the top circuit board 1102 and bottomcircuit board 1101 into reliable solder joint 1124 (FIG. 19).

Further Embodiments

In an embodiment the invention includes a method of connecting aplurality of flexible circuit boards together comprising the steps ofapplying a solder composition between an upper surface of a firstflexible circuit board and a lower surface of a second flexible circuitboard; holding the upper surface of the first flexible circuit board andthe lower surface of the second flexible circuit board together; andreflowing the solder composition with a heat source to bond the firstflexible circuit board and the second flexible circuit board together toform a flexible circuit board strip having a length longer than eitherof the first flexible circuit board or second flexible circuit boardseparately. In an embodiment, the method further comprises applying asolder composition between an upper surface of the second flexiblecircuit board and a lower surface of a third flexible circuit board andholding the upper surface of the second flexible circuit board and thelower surface of the third flexible circuit board together. In anembodiment, the method further comprises applying a solder compositionbetween an upper surface of the third flexible circuit board and a lowersurface of a fourth flexible circuit board and holding the upper surfaceof the third flexible circuit board and the lower surface of the fourthflexible circuit board together. In an embodiment, the method furthercomprises positioning a plurality of components on at least one of thefirst and second flexible circuit boards. In an embodiment, theplurality of components can include light emitting diodes. In anembodiment, the method further comprises positioning the plurality ofcomponents on the first and second flexible circuit boards takes placebefore the step of reflowing the solder composition with a heat sourceand the plurality of components are bonded to at least one of the firstand second flexible circuit boards during the step of reflowing thesolder composition with a heat source. In an embodiment, holding theupper surface of the first flexible circuit board and the lower surfaceof the second flexible circuit board together is achieved by positioninga clamp to contact the first flexible circuit board and the secondflexible circuit board. In an embodiment, the clamp comprises a u-shapedfastener, a spring tension arm connected to the u-shaped fastener, andan attachment hook connected to the spring tension arm. In anembodiment, the heat source delivers heat from the bottom of the firstand second flexible circuit boards. In an embodiment, the heat sourcedelivers heat from the top of the first and second flexible circuitboards. In an embodiment, the heat source delivers heat from the bottomand top of the first and second flexible circuit boards. In anembodiment, the solder composition is selected from the group consistingof solder, solder paste, and solder with flux. In an embodiment,reflowing the solder composition with a heat source results in solderflowing up through a hole in the first flexible circuit board. In anembodiment, the step of confirming bonding of the first flexible circuitboard and the second flexible circuit board together by inspection ofthe solder having flowed up through the hole. In an embodiment,inspection is conducted with a video sensor. In an embodiment, theformation of a dome shaped solder bead atop the hole confirms properbonding of the first flexible circuit board and the second flexiblecircuit board together. In an embodiment, the method further includesmeasuring the height of solder that has flowed up through the hole. Inan embodiment, the first and second flexible circuit boards are eachpart of arrays of circuit boards arranged parallel to one another.

In an embodiment, the invention includes a circuit board clamp forholding flexible circuit boards together. The clamp can include au-shaped fastener, a spring tension arm connected to the u-shapedfastener, and an attachment mechanism connected to the spring tensionarm. In an embodiment, the u-shaped fastener comprises a top bar portionand a bottom bar portion, the bottom bar comprising an end portion bentaway from the top bar. In an embodiment, the clamp is formed from aflexible wire. In an embodiment, the spring tension arm is connected tothe top bar portion of the u-shaped fastener. In an embodiment, thespring tension arm has a major axis oriented perpendicularly to the topbar portion of the u-shaped fastener. In an embodiment, the attachmentmechanism comprises an attachment hook.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the content clearly dictates otherwise. Thus, for example,reference to a composition containing “a compound” includes a mixture oftwo or more compounds. It should also be noted that the term “or” isgenerally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

It should also be noted that, as used in this specification and theappended claims, the phrase “configured” describes a system, apparatus,or other structure that is constructed or configured to perform aparticular task or adopt a particular configuration to. The phrase“configured” can be used interchangeably with other similar phrases suchas arranged and configured, constructed and arranged, constructed,manufactured and arranged, and the like.

All publications and patent applications in this specification areindicative of the level of ordinary skill in the art to which thisinvention pertains. All publications and patent applications are hereinincorporated by reference to the same extent as if each individualpublication or patent application was specifically and individuallyindicated by reference.

The invention has been described with reference to various specific andpreferred embodiments and techniques. However, it should be understoodthat many variations and modifications may be made while remainingwithin the spirit and scope of the invention.

The invention claimed is:
 1. A method of connecting a plurality offlexible circuit boards together comprising: applying a soldercomposition between first electrical contacts of a first portion of afirst flexible circuit board and second electrical contacts of a firstportion of a second flexible circuit board; positioning a clamp to holdthe first portion of the first flexible circuit board and the firstportion of the second flexible circuit board together such that theclamp does not contact the second electrical contacts which are exposedon a second portion of the second flexible circuit board, wherein theclamp contacts two opposite surfaces of the plurality of flexiblecircuit boards, wherein the clamp also does not apply pressure to bothsides of the solder composition; and reflowing the solder compositionwith a heat source to bond the first flexible circuit board and thesecond flexible circuit board together to form a flexible circuit boardstrip having a length longer than either of the first flexible circuitboard or second flexible circuit board separately.
 2. The method ofclaim 1, further comprising applying a solder composition between thesecond portion of the second flexible circuit board and a first portionof a third flexible circuit board; and positioning a clamp to hold thesecond portion of the second flexible circuit board and the firstportion of the third flexible circuit board together.
 3. The method ofclaim 1, further comprising applying a solder composition between asecond portion of the third flexible circuit board and a first portionof a fourth flexible circuit board; and holding the second portion ofthe third flexible circuit board and the first portion of the fourthflexible circuit board together.
 4. The method of claim 1, furthercomprising positioning a plurality of components on at least one of thefirst and second flexible circuit boards.
 5. The method of claim 4, thecomponents comprising light emitting diodes.
 6. The method of claim 4,wherein positioning the plurality of components on the first and secondflexible circuit boards takes place before the step of reflowing thesolder composition with a heat source and the plurality of componentsare bonded to at least one of the first and second flexible circuitboards during the step of reflowing the solder composition with a heatsource.
 7. The method of claim 1, the clamp comprising a u-shapedfastener, a spring tension arm connected to the u-shaped fastener, andan attachment hook attached to the spring tension arm.
 8. The method ofclaim 1, wherein the heat source delivers heat from the bottom of thefirst and second flexible circuit boards.
 9. The method of claim 1,wherein the heat source delivers heat from the top of the first andsecond flexible circuit boards.
 10. The method of claim 1, wherein theheat source delivers heat from the bottom and top of the first andsecond flexible circuit boards.
 11. The method of claim 1, wherein thesolder composition is selected from the group consisting of solder,solder paste, and solder with flux.
 12. The method of claim 1, furthercomprising the step of confirming bonding of the first flexible circuitboard and the second flexible circuit board together by inspection ofthe solder having flowed through a hole in the first flexible circuitboard.
 13. The method of claim 12, wherein the formation of a domeshaped solder bead atop the hole confirms proper bonding of the firstflexible circuit board and the second flexible circuit board together.14. The method of claim 1, wherein the first and second flexible circuitboards are each part of arrays of circuit boards arranged parallel toone another.
 15. A method of connecting a plurality of flexible circuitboards together comprising: applying a solder composition between firstelectrical contacts of a first portion of a first flexible circuit boardand second electrical contacts of a first portion of a second flexiblecircuit board; positioning a clamp to hold the first portion of thefirst flexible circuit board and the first portion of the secondflexible circuit board together such that the clamp contacts twoopposite surfaces of the plurality of flexible circuit boards and theclamp does not contact the second electrical contacts which are exposedon a second portion of the second flexible circuit board; and reflowingthe solder composition with a heat source to bond the first flexiblecircuit board and the second flexible circuit board together to form aflexible circuit board strip having a length longer than either of thefirst flexible circuit board or second flexible circuit boardseparately, wherein the solder composition is exposed and configured tobe visually inspected from a perspective that is perpendicular to asurface of the first flexible circuit board or a surface of the secondflexible circuit board which comprises at least one of the electricalcontacts after bonding the first flexible circuit board with the secondflexible circuit board.
 16. The method of claim 15, further comprisingapplying a solder composition between the second portion of the secondflexible circuit board and a first portion of a third flexible circuitboard; and positioning a clamp to hold the second portion of the secondflexible circuit board and the first portion of the third flexiblecircuit board together.
 17. The method of claim 16, further comprisingrolling the first flexible circuit board, the second flexible circuitboard, and third flexible circuit board into reel form.
 18. A method ofconnecting a plurality of flexible circuit boards together comprising:applying a solder composition between first electrical contacts of afirst portion of a first flexible circuit board and second electricalcontacts of a first portion of a second flexible circuit board;positioning a clamp to hold the first portion of the first flexiblecircuit board and the first portion of the second flexible circuit boardtogether such that the clamp contacts two opposite surfaces of theplurality of flexible circuit boards and the clamp does not interferewith visual inspection of a bond between the first flexible circuitboard and the second flexible circuit board, wherein the visualinspection is from a perspective that is perpendicular to a surface ofthe first flexible circuit board or a surface of the second flexiblecircuit board which comprises at least one of the electrical contacts;and reflowing the solder composition with a heat source to bond thefirst flexible circuit board and the second flexible circuit boardtogether to form a flexible circuit board strip having a length longerthan either of the first flexible circuit board or second flexiblecircuit board separately.